Optical node device

Abstract

This optical node device comprises: a first wavelength conversion unit (11) that receives an input of an optical signal of a first wavelength and first excitation light, and converts the input signal light into an optical signal of a second wavelength by a nonlinear optical effect; an optical signal processing unit (12) that subjects the optical signal converted into the optical signal of the second wavelength to predetermined optical signal processing; a second wavelength conversion unit (13) that receives an input of the optical signal subjected to the optical signal processing and second excitation light, and converts the input signal light into an optical signal of the first wavelength by the nonlinear optical effect; an excitation light generation unit (14) that outputs the first excitation light and second excitation light generated by splitting excitation light generated from a single light source; and a delay adjustment unit (15) that adjusts delay of the second excitation light in line with the first excitation light.

Description

Optical node equipment

[0001] The present invention relates to an optical node device.

[0002] In recent years, communication traffic has been increasing exponentially with the launch of the 5th Generation Mobile Communication System and the widespread use of rich content such as high-resolution video. This has led to a demand for continuous increases in the communication capacity of optical transmission systems. In optical fiber transmission, the transmission capacity per optical fiber can be improved by widening the optical transmission band. Therefore, various studies are being conducted to realize ultra-wideband wavelength division multiplexing transmission.

[0003] The wavelength range with low transmission loss in optical fibers is divided into several optical transmission bands. Long-distance optical fiber communication networks primarily use the C-band or L-band, which has the lowest transmission loss among all optical transmission bands, from approximately 4 THz to 5 THz. This optical transmission band can utilize high-performance optical amplifier repeaters, such as erbium-doped fiber amplifiers (EDFAs).

[0004] In order to broaden the optical transmission band, in addition to the combined use of the C-band and L-band, there has been active research and development into ultra-wideband wavelength division multiplexing transmission systems that use new optical transmission bands such as the S-band and U-band. Such wideband transmission systems that use multiple optical transmission bands are called multiband transmission systems. Multiband transmission systems require the development of new transponders that support optical transmission bands that have not been used before.

[0005] In addition to optical fibers and optical transceivers, optical node devices (optical node units) are also used for the transmission paths of optical signals in long-distance optical transmission systems. Optical node devices can amplify optical signals as they are, and perform add / drop and routing of wavelength channels. Optical node devices that perform add / drop of wavelength channels are called ROADMs (Reconfigurable Optical Add-Drop Multiplexers). Optical node devices that switch wavelength paths for multi-directional routes are called optical cross connects (OXCs).

[0006] ROADMs and optical cross connects (OXCs) use wavelength selective switches (WSSs) to switch the wavelength channel routes. To convert the wavelength of a channel, an optical transceiver converts the optical signal into an electrical signal, receives the electrical signal, and then modulates it again to a new wavelength. In multiband transmission systems, the wavelength selective switch (WSS) must be adaptable to not only conventional optical transmission bands but also multiple new optical transmission bands. Furthermore, as the number of wavelength channels increases, the number of transponders required for wavelength conversion also increases, resulting in issues such as increased costs associated with devices such as power consumption and an increase in the scale of the optical transmission system.

[0007] Against this background, all-optical wavelength conversion technologies using nonlinear optical effects have recently attracted attention. For example, representative technologies under consideration include wavelength conversion using four-wave mixing (FWM), a third-order nonlinear optical effect, and wavelength conversion using differential frequency generation (DFG), a second-order nonlinear optical effect (see Patent Document 1). Wavelength conversion using cross-phase modulation and cross-gain modulation effects by semiconductor optical amplifiers is also being considered.

[0008] In particular, wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect, and wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect, are capable of wavelength conversion over a wide band. Methods using four-wave mixing and difference frequency generation are capable of simultaneously converting wavelength multiplexed signals from one optical transmission band to a different optical transmission band. By utilizing such wideband wavelength band conversion and configuring a wavelength multiplexed signal to be generated in a conventionally used optical transmission band (e.g., C-band) and then converted to another optical transmission band, multiband transmission can be realized without the need to prepare a new optical transceiver adapted to the new optical transmission band (see Non-Patent Document 1).

[0009] In optical node devices, by simultaneously converting all channels to a conventionally used optical transmission band (e.g., C-band), optical amplifiers for existing optical transmission bands, such as wavelength selective switches (WSS) and erbium-doped optical fiber amplifiers (EDFA), can be used for channels of other optical transmission bands. This also enables low-latency, low-power wavelength conversion without the use of optical transceivers (i.e., without optical-to-electrical conversion). For example, each channel that has been wavelength-band converted by a wavelength selective switch (WSS) or other wavelength band converter in the C-band is reconverted to the original optical transmission band by another wavelength band converter.

[0010] In wavelength conversion using four-wave mixing, a third-order nonlinear optical effect, pump light is placed between the signal light and the wavelength-converted light. In wavelength conversion using difference frequency generation, a second-order nonlinear optical effect, pump light of a second harmonic, which has a frequency twice that of the frequency between the signal light and the wavelength-converted light, is used. It is also difficult to directly prepare high-power pump light of a second harmonic. Therefore, a configuration is used in which light having a frequency between the signal light and the wavelength-converted light is amplified by a high-power optical amplifier such as an erbium-doped optical fiber amplifier (EDFA), and then converted into a second harmonic using the second harmonic generation (SHG) process in a second-order nonlinear medium. Hereinafter, the pump light before being converted into a second harmonic is referred to as the "fundamental pump light."

[0011] In wavelength conversion using four-wave mixing, a third-order nonlinear optical effect, stimulated Brillouin scattering and phase modulation of the pump light can cause signal distortion and distortion of the conversion efficiency spectrum. To suppress stimulated Brillouin scattering, a method of modulating phase dither with the pump light is used, but the phase noise and frequency fluctuation of the pump light are transmitted to the wavelength-converted light, so the effect of phase dither on the signal becomes an issue.

[0012] In wavelength conversion using difference frequency generation (DFR), a second-order nonlinear optical effect, the influence of stimulated Brillouin scattering is small in principle, so phase dithering is generally not necessary. On the other hand, as with wavelength conversion using four-wave mixing (FWM), a third-order nonlinear optical effect, the phase noise and frequency fluctuation of the pump light are transmitted to the wavelength-converted light, so it is desirable that the linewidth and frequency noise of the pump light source be as small as possible.

[0013] Japanese Patent Application Laid-Open No. 2020-86031

[0014] T. Kato, H. Muranaka, Y. Tanaka, Y. Akiyama, T. Hoshida, S. Shimizu, T. Kobayashi, T. Kazama, T. Umeki, K. Watanabe, and Y. Miyamoto, “S+C+L-Band WDM Transmission Using 400-Gb / s Real-Time Transceivers Extended by PPLN-Based Wavelength Converter,” Proceeding of European Conference on Optical Communication (ECOC), We4D.4, September 2022

[0015] In long-distance optical transmission networks, optical signals are transmitted through multiple optical node devices (optical node units). In optical node configurations that perform wavelength band conversion, optical signals undergo multiple wavelength band conversions before reaching the receiving end. As a result, optical signals are transmitted multiple times, including the phase noise and frequency fluctuations they experience from the pump light. Suppressing the degradation of signal characteristics due to the transmission of such phase noise is an important issue when applying all-optical wavelength conversion technology using nonlinear optical effects in optical node devices (optical node units), etc.

[0016] The present invention has been made in view of the above-described technical background, and aims to provide a technology that can perform optical signal processing via wavelength conversion while maintaining good signal quality by canceling out phase noise transmitted from pump light to signal light.

[0017] One aspect of the present invention is an optical node device comprising: a first wavelength conversion unit that receives input of an optical signal of a first wavelength and first excitation light and converts the input signal light into the optical signal of a second wavelength by a nonlinear optical effect; an optical signal processing unit that performs predetermined optical signal processing on the optical signal converted into the optical signal of the second wavelength; a second wavelength conversion unit that receives input of the optical signal that has been subjected to the optical signal processing and second excitation light and converts the input signal light into the optical signal of the first wavelength by the nonlinear optical effect; an excitation light generation unit that outputs the first excitation light and the second excitation light that are generated by branching excitation light generated from a single light source; and a delay adjustment unit that adjusts the delay of the second excitation light to match the first excitation light.

[0018] According to the present invention, it is possible to perform optical signal processing via wavelength conversion while maintaining good signal quality by canceling out phase noise transferred from pump light to signal light.

[0019] FIG. 1 is a diagram showing wavelength conversion by optical parametric amplification. FIG. 2 is a diagram showing the basic configuration of an optical node device 1 in a first embodiment of the present invention. FIG. 3 is a diagram showing the basic configuration of an optical node device 1a in a first embodiment of the present invention. FIG. 4 is a detailed configuration diagram of an optical node device assuming wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect. Graph showing a comparison of the signal quality of wavelength-converted light between a configuration according to the present invention and a configuration using an independent pumping light source. FIG. 5 is a diagram showing the basic configuration of an optical node device 1c in a second embodiment of the present invention. FIG. 6 is a diagram showing the basic configuration of an optical node device 1d in a third embodiment of the present invention.

[0020] Hereinafter, an optical node device according to an embodiment will be described with reference to the drawings.

[0021] As mentioned above, suppressing the degradation of signal characteristics due to the transmission of phase noise is an important issue when applying all-optical wavelength conversion technology using nonlinear optical effects in optical node equipment. ｉ is expressed as the following equations (1) and (2).

[0022]

[0023]

[0024] Here, "E ｓ " represents the time waveform of the input signal light. ｓ " represents the complex amplitude of the modulating signal. ｏ " represents a phase offset resulting from the relative phase difference between the pump light and the signal carrier, etc. "j" represents the imaginary unit. "*" represents the complex conjugate.

[0025] In addition, the angular frequency ω of the wavelength-converted light ｉ is ω ｉ = 2ω ｐ -ω ｓ Here, "ω ｐ " represents the angular frequency of the excitation light. "ω ｓ " represents the angular frequency of the signal light.

[0026] In the case of wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect, the pump light here refers to the fundamental pump light before being converted into a second harmonic by the second harmonic generation (SHG) process. Note that here, the effects of noise components originally present in the signal band and vacuum noise amplified during the wavelength conversion process are ignored. Also, here, the effects of pump depletion and optical loss in the nonlinear medium are ignored. After reconversion to the original frequency ω ｓ The complex amplitude E of the electric field of the optical signal returned to ｓ ' is expressed as the following equation (3).

[0027]

[0028] Here, "φ ｏ '" is the phase offset at the time of reconversion added to the original phase offset. On the other hand, when the frequency noise Δω(t) of the fundamental pump light is taken into consideration, Equation (2) can be expressed as the following Equation (4).

[0029]

[0030] Similarly, when the fundamental pump light having frequency noise Δω′(t) is reconverted, Equation (3) can be expressed as Equation (5) below.

[0031]

[0032] Therefore, the signal light is imparted with frequency noise originating from the pump light. This frequency noise not only causes a frequency offset during coherent detection, but is also known to be converted into excess noise such as group delay jitter through interaction with chromatic dispersion occurring in the transmission line.

[0033] In order to solve the above problems, the optical node device according to the embodiment of the present invention described below has a configuration that suppresses the transmission of phase noise from pump light. From the above equation (5), if Δω(t) = Δω'(t), the frequency noise is canceled out when the optical signal is reconverted, and an optical signal without excess noise can be obtained.

[0034] The correlation of frequency noise in laser light is defined by coherence. There is no correlation between frequency noise in two laser lights emitted from different light sources. On the other hand, whether coherence is maintained between two laser lights emitted from a single light source and branched depends on the delay difference between the two branched paths. The delay difference at which coherence is maintained is called the "coherence length." If the delay difference is within the coherence length, there is a phase correlation between the two branched laser lights according to the delay difference.

[0035] By utilizing this property, the optical node device of the present invention uses two laser beams emitted from a single light source and branched into two beams as excitation light between a pair of wavelength converters. The optical node device of the present invention is equipped with a configuration for adjusting the delay difference between these two excitation beams, thereby suppressing degradation of optical signals passing through the optical node device.

[0036] In applications such as ROADM, where wavelength conversion and reconversion are performed at one point, coherence of the pump light can be maintained between the two wavelength converters by using two laser beams branched from a single light source as pump light. The complex amplitude of the electric field of the wavelength-converted light that has been wavelength-converted by a wavelength converter at a previous stage and processed by a wavelength selective switch (WSS) or the like and then reaches the wavelength converter at a subsequent stage is expressed as the delay time τ from the output end of the wavelength converter at the previous stage to the input end of the wavelength converter at the subsequent stage. １ Then, it is expressed as the following equation (6).

[0037]

[0038] On the other hand, if the two pump lights are coherent, the electric field complex amplitude Es′ of the wavelength-converted light after reconversion is expressed by the following equation (7).

[0039]

[0040] Here, "τ ２ ” is the delay time difference between the paths of the two excitation light frequency noise components. １ = τ ２By adjusting the delay difference between the two pump lights by a physical delay line or the like so that:

[0041] In order to compensate for frequency noise in the high frequency band, the delay must be adjusted with extremely high precision in order to compensate for the frequency noise sufficiently. However, it is known that the contribution of frequency noise in the high frequency band to the signal is not large and can be ignored to a certain extent. On the other hand, frequency noise in the low frequency band can be compensated for sufficiently.

[0042] Generally, the Lorentz linewidth of a laser light source is defined by the white noise floor of the frequency noise spectrum. The frequency noise of laser light includes not only white noise but also colored noise in the low frequency band. This colored noise originates from the structure of the laser resonator and the wavelength stabilization mechanism, etc. Once the colored noise in the low frequency band is compensated for, the remaining frequency noise will mainly originate from white noise. This has the advantage of making it possible to uniformly specify the specifications of the pump light in terms of the Lorentz linewidth.

[0043] First Embodiment An optical node device 1 according to a first embodiment of the present invention will be described below with reference to FIGS.

[0044] FIG. 1 is a diagram showing wavelength conversion by an optical parametric amplifier (OPA). １ ~E ５ represents each channel of a wavelength division multiplexing (WDM) signal.

[0045] When signal light is input into an optical parametric amplifier (OPA), idler light, which is phase conjugate light, is generated at a frequency symmetrical to the degenerate frequency. In other words, the idler light is generated with the spectral arrangement of the input wavelength division multiplexed (WDM) signal reversed. While it is sufficient to extract either one of the band components for the transmission signal, extracting the band component of the idler light makes it possible to perform simultaneous wavelength conversion of wavelength division multiplexed (WDM) signals.

[0046] 2 is a basic configuration diagram of the optical node device 1 according to the first embodiment of the present invention. As shown in FIG. 2, the optical node device 1 includes a first wavelength converter 11, an optical signal processor 12, a second wavelength converter 13, an excitation light generator 14, and a delay adjuster 15.

[0047] The optical signal is input to the first wavelength converter 11. The first wavelength converter 11 also receives first pumping light output from a pumping light generator 14 (described later). The first wavelength converter 11 converts the wavelength of the input optical signal using the first pumping light. The first wavelength converter 11 outputs the wavelength-converted optical signal to the optical signal processor 12.

[0048] The optical signal output from the first wavelength converter 11 is input to the optical signal processing unit 12. The optical signal processing unit 12 corresponds to the band after wavelength conversion by the first wavelength converter 11. The optical signal processing unit 12 performs optical signal processing on the input optical signal. The optical signal processing here refers to wavelength add / drop, routing, gain equalization, etc. of optical channels using a wavelength selective switch (WSS). The optical signal processing unit 12 outputs the optical signal that has undergone optical signal processing to the second wavelength converter 13.

[0049] The second wavelength converter 13 receives the optical signal output from the optical signal processing unit 12. The second wavelength converter 13 also receives second pump light output from the delay adjustment unit 15 (described later). The second wavelength converter 13 wavelength-converts the input optical signal and reconverts it to the original wavelength band. The second wavelength converter 13 outputs the optical signal reconverted to the original wavelength band.

[0050] In this way, optical signal processing is performed by the optical signal processing unit 12 arranged between the pair of wavelength conversion units (the first wavelength conversion unit 11 and the second wavelength conversion unit 13). Note that, as in the optical node device 1a shown in Fig. 3, it is also possible to configure optical amplification relay using an optical amplifier (optical amplification unit 16) manufactured for an existing band, such as an erbium-doped optical fiber amplifier (EDFA).

[0051] The pump light generation unit 14 generates pump light for the optical parametric amplification process in each wavelength conversion unit (i.e., each of the first wavelength conversion unit 11 and the second wavelength conversion unit 13). The pump light generation unit 14 outputs the first pump light to the first wavelength conversion unit 11 and outputs the second pump light to the delay adjustment unit 15. In this way, the first pump light and the second pump light are pump light emitted from the same pump light source.

[0052] The second pumping light output from the pumping light generating unit 14 is input to the delay adjusting unit 15. The delay adjusting unit 15 adjusts the delay of the pumping light to be output to the second wavelength converting unit 13 according to the delay adjustment method described above.

[0053] The delay amount is controlled by using an optical fiber of an appropriate length so that each communication path has an appropriate optical path length. However, the control method is not limited to this, and the delay amount may be controlled by using, for example, a variable optical fiber stretcher using a piezoelectric element or the like, or a variable delay line using a spatial optical system or the like.

[0054] For delay adjustment, the optical path length of each communication path is directly measured and τ １ = τ ２ However, the adjustment method is not limited to this, and for example, a method may be used in which the frequency noise spectrum of the signal light wavelength-converted by the second wavelength converter 13 is measured and adjusted to match the frequency noise spectrum of the signal light before wavelength conversion (i.e., the signal light input to the first wavelength converter 11). The frequency noise spectrum can be measured by a method using a self-delayed heterodyne interferometer, for example.

[0055] 4 is a detailed configuration diagram of an example of an optical node device assuming wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect. As shown in Fig. 4, the optical node device 1b includes a polarization demultiplexing unit 101, an excitation light multiplexing unit 102, a nonlinear medium 103, an excitation light branching unit 104, a polarization multiplexing unit 105, a wavelength conversion light extraction filter 106, an optical signal processing unit 107, an excitation light source 108, an excitation light branching unit 109, an optical amplifier 110, a delay adjustment unit 111, a second delay adjustment unit 112, and a third delay adjustment unit 113.

[0056] Wavelength conversion using difference frequency generation, a second-order nonlinear optical effect, uses pump light of the second harmonic, which has a frequency twice the center frequency of the gain band. It is difficult to directly prepare high-power pump light of the second harmonic. Therefore, a configuration is used in which light with a frequency between the signal light and the wavelength-converted light is amplified by a high-power optical amplifier such as an erbium-doped optical fiber amplifier (EDFA), and then converted into a second harmonic by utilizing the second-harmonic generation (SHG) process in a second-order nonlinear medium.

[0057] Furthermore, since the nonlinear optical effect is polarization dependent, a polarization diversity configuration is used to make the optical signal polarization independent. The input optical signal is first split into two orthogonal polarization components by a polarization beam splitter or the like. The signal light split into the two orthogonal polarization components is then multiplexed with pump light, and wavelength conversion is performed in each nonlinear medium 103. The pump light is then separated from the signal light, and polarization multiplexing is performed again. The multiplexing and splitting of the pump light is performed using, for example, a wavelength multiplexing filter made of a dielectric multilayer film or the like, or a dichroic mirror or the like.

[0058] The light from the output end of the nonlinear medium 103 contains both the wavelength-converted light and the signal light in the original wavelength band. Therefore, a filter that attenuates the signal light in the original wavelength band and extracts only the wavelength-converted light is used at the output of the polarization multiplexer 105. This filter may be, for example, a wavelength multiplexing filter made of a dielectric multilayer film or a wavelength selective switch (WSS).

[0059] The optical signal processing unit 107 performs optical signal processing on the wavelength-converted signal light. After that, the optical signal is converted back to the original wavelength band through wavelength conversion using a polarization diversity configuration again. At this time, the pump light is laser light from one pump light source 108 shared by all of the nonlinear media 103.

[0060] Therefore, in the configuration shown in Fig. 4, the pump light is split into four. Therefore, in order to cancel out the phase noise transferred from the pump light to the wavelength-converted light, it is necessary to adjust the paths of these four pump lights so that they each have an appropriate optical path length. Therefore, after the optical path lengths of the two pump lights used in each polarization diversity configuration are aligned, the delay between the two wavelength converters is adjusted to τ １ = τ ２ It needs to be adjusted so that

[0061] An example will be described below. Fig. 5 is a graph showing the results of comparing the signal quality of wavelength-converted light when wavelength conversion and reconversion are performed using the configuration of the first embodiment described above (i.e., using pumping light emitted from one pumping light source and branched), and when wavelength conversion and reconversion are performed using independent pumping light (i.e., using pumping light emitted from different pumping light sources). Here, as an example, wavelength conversion and reconversion were performed for each amplification repeater in a transmission system with a transmission interval of 30 [km] using a 96 Gbaud polarization multiplexed 64 QAM signal, and a comparison was made.

[0062] In the graph shown in Figure 5, the horizontal axis represents the number of amplification repeats, and the vertical axis represents the signal-to-noise ratio (SNR, unit: dB). The number of passes through wavelength converters corresponds to twice the number of amplification repeats. From the results of this example, it was confirmed that when wavelength conversion and reconversion are performed using the configuration of the first embodiment described above, transmission quality is improved compared to when wavelength conversion and reconversion are performed using independent pump light. For example, when passing through two wavelength converters, an improvement in transmission quality of just under 1 [dB] was confirmed, and when passing through 28 wavelength converters, an improvement in transmission quality of approximately 3 [dB] was confirmed.

[0063] Second Embodiment An optical node device 1c according to a second embodiment of the present invention will now be described with reference to FIG.

[0064] 6 is a basic configuration diagram of an optical node device 1c according to a second embodiment of the present invention. As shown in Fig. 6, the optical node device 1c includes a first wavelength converter 11, an optical signal processor 12, a second wavelength converter 13, an excitation light generator 14, a delay adjuster 15, and two optical amplifiers 16.

[0065] The configuration of the optical node device 1c in the second embodiment is a configuration in which optical amplifiers 16 are added to the front stage of the optical signal processing unit 12 and the rear stage of the second wavelength conversion unit 13, in comparison with the configuration of the optical node device 1c in the first embodiment described above. The following description will focus on the differences from the configuration of the optical node device 1 in the first embodiment.

[0066] Optical signal loss occurs in the optical signal processing unit 12, which is configured using a wavelength selective switch (WSS) or the like. Therefore, in order to avoid excessive degradation of the optical signal-to-noise ratio (OSNR) of the optical signal, it is desirable to amplify the optical signal in advance before performing optical signal processing. Wavelength conversion using nonlinear optical effects can simultaneously undergo amplification through the optical parametric amplification process. Therefore, when the pump light is sufficiently strong, the wavelength-converted signal light is output in a state where the optical power is increased (amplified state) compared to the original signal light. By utilizing this amplification gain, the optical node device 1c in the second embodiment can suppress degradation of the optical signal-to-noise ratio (OSNR) due to optical loss in the optical signal processing unit 12.

[0067] On the other hand, it is known that when the optical power output from the second wavelength converter 13 is large, distortion occurs in the modulated signal due to nonlinear amplification gain that occurs in the optical parametric amplification process. In order to avoid this effect and suppress deterioration of the optical signal-to-noise ratio (OSNR) due to optical loss in the optical signal processor 12, the optical node device 1c in the second embodiment is provided with an optical amplifier 16 between the first wavelength converter 11 and the optical signal processor 12, as shown in FIG.

[0068] In this case, an optical amplifier that does not cause distortion in the modulated signal even in a high output range, such as an erbium-doped optical fiber amplifier (EDFA), is used for the optical amplification unit 16. This allows the optical node device 1c in the second embodiment to suppress deterioration of the optical signal-to-noise ratio (OSNR) due to optical loss in the optical signal processing unit 12.

[0069] Furthermore, in the case of a configuration in which an optical signal is reconverted to the original signal band by a second wavelength conversion unit 13 and then input to a transmission path, as in the optical node device 1c shown in Figure 6, it is desirable to also provide an optical amplification unit 16 using an optical amplifier such as an erbium-doped optical fiber amplifier (EDFA) in the stage following the second wavelength conversion unit 13.

[0070] Third Embodiment An optical node device 1d according to a third embodiment of the present invention will now be described with reference to FIG.

[0071] 7 is a basic configuration diagram of an optical node device 1d according to a third embodiment of the present invention. As shown in Fig. 7, the optical node device 1d includes a first wavelength converter 11, an optical signal processor 12, a second wavelength converter 13, an excitation light generator 14, a delay adjuster 15, and four optical amplifiers 16.

[0072] The configuration of the optical node device 1d in the third embodiment is the same as the configuration of the optical node device 1c in the second embodiment described above, except that optical amplifiers 16 are added before the first wavelength converter 11 and before the second wavelength converter 13. The following description will focus on the differences from the configuration of the optical node device 1c in the second embodiment.

[0073] If the conversion efficiency of the first wavelength converter 11 and the second wavelength converter 13 is low and the optical power of the wavelength-converted light is smaller than the original input signal light, then, as with the optical node device 1c in the second embodiment described above, excessive deterioration of the optical signal-to-noise ratio (OSNR) may occur in the first wavelength converter 11 and the second wavelength converter 13. In order to prevent the optical power of the signal light output from the first wavelength converter 11 and the second wavelength converter 13 from becoming weak, the optical node device 1d in the third embodiment is also provided with optical amplifiers 16 upstream of the first wavelength converter 11 and the second wavelength converter 13, as shown in FIG.

[0074] As described above, the optical node devices 1, 1a to 1d in each embodiment of the present invention are configured to share pump light between two wavelength conversion units (the first wavelength conversion unit 11 and the second wavelength conversion unit 13) and perform delay adjustment. This allows the optical node devices 1, 1a to 1d in each embodiment of the present invention to cancel out the transfer of phase noise from the pump light to the wavelength-converted light, and to perform various optical signal processing via wavelength conversion while maintaining good signal quality.

[0075] According to the above-described embodiment, the optical node device includes a first wavelength converter, an optical signal processing unit, a second wavelength converter, an excitation light generation unit, and a delay adjustment unit. For example, the optical node device is the optical node device 1, 1a to 1d in the embodiment, the first wavelength converter is the first wavelength converter 11 in the embodiment, the optical signal processing unit is the optical signal processing unit 12 in the embodiment, the second wavelength converter is the second wavelength converter 13 in the embodiment, the excitation light generation unit is the excitation light generation unit 14 in the embodiment, and the delay adjustment unit is the delay adjustment unit 15 in the embodiment.

[0076] The first wavelength conversion unit receives an input of an optical signal of a first wavelength and first pump light, and converts the input signal light into an optical signal of a second wavelength by a nonlinear optical effect. The optical signal processing unit performs predetermined optical signal processing on the optical signal converted into the optical signal of the second wavelength. The second wavelength conversion unit receives an input of the optical signal that has been subjected to optical signal processing and the second pump light, and converts the input signal light into an optical signal of the first wavelength by a nonlinear optical effect. The pump light generation unit outputs first pump light and second pump light generated by branching pump light generated from a single light source. The delay adjustment unit adjusts the delay of the second pump light to match the first pump light.

[0077] The optical node device may perform at least one of wavelength add / drop, optical path routing, gain equalization, and optical amplification.

[0078] The optical node device may further include a first optical amplifier and a second optical amplifier. The first optical amplifier is disposed between the first wavelength converter and the optical signal processor and amplifies the optical signal. The second optical amplifier is disposed between the optical signal processor and the second wavelength converter and amplifies the optical signal.

[0079] The optical node device may further include a third optical amplifier and a fourth optical amplifier. The third optical amplifier is disposed before the first wavelength converter and amplifies the optical signal. The fourth optical amplifier is disposed before the wavelength converter and amplifies the optical signal.

[0080] Based on the above-described embodiment, the optical node device of the present invention can be configured as follows.

[0081] (1) An optical node device comprising: a first wavelength conversion unit that performs wavelength conversion of an optical signal all-optically using a nonlinear optical effect of a nonlinear optical medium; an optical signal processing unit that performs optical signal processing on the optical signal wavelength-converted by the first wavelength conversion unit; a second wavelength conversion unit that uses the nonlinear optical effect to all-optically wavelength-convert the optical signal that has been subjected to the optical signal processing by the optical signal processing unit and reconvert it to its original band; a pumping light generation unit that generates first pumping light and second pumping light for nonlinear optical processes in the first wavelength conversion unit and the second wavelength conversion unit, the first pumping light and second pumping light being obtained by branching a laser light source emitted from the same light source; and a delay adjustment unit that adjusts the path length of the first pumping light and the second pumping light to the first wavelength conversion unit and the second wavelength conversion unit.

[0082] (2) The optical node device according to (1), wherein the optical signal processing unit performs at least one process of wavelength add / drop, optical path routing, gain equalization, and optical amplification.

[0083] (3) The optical node device according to (1), further comprising: a first optical amplifier arranged between the first wavelength converter and the optical signal processor; and a second optical amplifier arranged between the optical signal processor and the second wavelength converter.

[0084] (4) The optical node device according to (3), further comprising: a third optical amplifier arranged in a stage preceding the first wavelength converter; and a fourth optical amplifier arranged in a stage preceding the second wavelength converter.

[0085] (5) The optical node device according to claim (4), wherein the first optical amplification unit, the second optical amplification unit, the third optical amplification unit, and the fourth optical amplification unit comprise at least one of a rare-earth doped fiber amplifier, a Raman amplifier, a semiconductor optical amplifier, and an optical parametric amplifier.

[0086] (6) The first wavelength conversion unit comprises: a polarization diversity configuration having a polarization splitter, a first nonlinear medium unit, a second nonlinear medium unit, and a first polarization multiplexer; a first pumping light branching unit that branches the first pumping light into third pumping light and fourth pumping light in order to generate the nonlinear optical processes in the first nonlinear medium unit and the second nonlinear medium unit, respectively; and a second delay adjustment unit that adjusts a delay between paths of the third pumping light and the fourth pumping light; and the second wavelength conversion unit comprises: a polarization diversity configuration having a polarization splitter, a third nonlinear medium unit, a fourth nonlinear medium unit, and a second polarization multiplexer; a second pumping light branching unit that branches the second pumping light into fifth pumping light and sixth pumping light in order to generate the nonlinear optical processes in the third nonlinear medium unit and the fourth nonlinear medium unit, respectively; and a third delay adjustment unit that adjusts a delay between paths of the fifth pumping light and the sixth pumping light. The optical node device according to (1) is provided with:

[0087] (7) The optical node device described in (1), wherein the first delay adjustment unit, the second delay adjustment unit, and the third delay adjustment unit measure the optical path lengths of the pumping light path and the signal light path, and based on the results of the measurement, control the delay amount so that the absolute values ​​of the pumping light phase component imparted to the signal light by the second wavelength conversion unit and the pumping light phase component imparted to the signal light by the first wavelength conversion unit are the same.

[0088] (8) The optical node device described in (1), wherein the first delay adjustment unit, the second delay adjustment unit, and the third delay adjustment unit measure the frequency noise spectrum of the signal light wavelength-converted by the second wavelength conversion unit, and based on the results of the measurement, control the amount of delay so that the frequency noise spectrum matches the frequency noise spectrum of the signal light before passing through the first wavelength conversion unit.

[0089] A portion of the configuration of the optical node devices 1, 1a-1d in the above-described embodiments may be implemented by a computer. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" herein includes hardware such as an OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or communication lines such as telephone lines, or devices that store programs for a certain period of time, such as volatile memory within the computer system that serves as the server or client in such cases. Furthermore, the program may be designed to implement a portion of the above-described functions, or may be capable of implementing the above-described functions in combination with a program already recorded in the computer system, or may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0090] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0091] DESCRIPTION OF SYMBOLS 1, 1a to 1d...optical node device, 11...first wavelength conversion unit, 12...optical signal processing unit, 13...second wavelength conversion unit, 14...pumping light generation unit, 15...delay adjustment unit, 16...optical amplification unit, 101...polarization demultiplexing unit, 102...pumping light multiplexing unit, 103...nonlinear medium, 104...pumping light branching unit, 105...polarization multiplexing unit, 106...wavelength conversion light extraction filter, 107...optical signal processing unit, 108...pumping light source, 109...pumping light branching unit, 110...optical amplifier, 111...delay adjustment unit, 112...second delay adjustment unit, 113...third delay adjustment unit

Claims

1. An optical node device comprising: a first wavelength conversion unit that receives an input of an optical signal of a first wavelength and a first excitation light, and converts the input signal light into an optical signal of a second wavelength by a nonlinear optical effect; an optical signal processing unit that performs a predetermined optical signal processing on the optical signal converted into the optical signal of the second wavelength; a second wavelength conversion unit that receives an input of the optical signal that has been subjected to the optical signal processing and a second excitation light, and converts the input signal light into the optical signal of the first wavelength by the nonlinear optical effect; an excitation light generation unit that outputs the first excitation light and the second excitation light that are generated by branching excitation light generated from a single light source; and a delay adjustment unit that adjusts the delay of the second excitation light to match the first excitation light.

2. The optical node device according to claim 1, wherein the optical signal processing unit performs at least one of the following processes: wavelength add / drop, optical path routing, gain equalization, and optical amplification.

3. The optical node device according to claim 1, further comprising: a first optical amplifier arranged between the first wavelength conversion unit and the optical signal processing unit, amplifying the optical signal; and a second optical amplifier arranged between the optical signal processing unit and the second wavelength conversion unit, amplifying the optical signal.

4. The optical node device according to claim 3, further comprising: a third optical amplifier arranged upstream of the first wavelength conversion unit for amplifying the optical signal; and a fourth optical amplifier arranged upstream of the second wavelength conversion unit for amplifying the optical signal.